This invention relates generally to safety links or devices for preventing hazardous falls by construction workers, and particularly to a safety device which may be removably attached to a slotted metal beam in a concrete pouring form and used by the worker to anchor a safety line or harness.
The safety device of this invention is particularly suited for use with slotted beams of the type used for erecting concrete pouring forms as shown and described in U.S. Pat. Nos. 3,899,152; 4,144,690; and 4,156,999 to Avery, as well as U.S. Pat. No. 4,033,544 to Johnston. To the extent that those patents are instructive as to the manufacture and assembly of the various components of those concrete pouring forms, the content of those disclosures are incorporated herein by reference.
In erecting the concrete pouring forms or "flying forms" as described, workers will generally climb on the horizontal beams and trusses surrounding the wooden forms and thereby use the beams as scaffolding, or hang scaffolding from those beams, to build the concrete pouring form from the bottom up. When a section of the concrete structure has been poured and cured sufficiently, the process of erecting the form may continue upwardly, or the form may be transferred or "flown" to a new location by crane.
As workers climb up the horizontal beams, they must be assembling components of the form by nailing, screwing, or bolting sections together. It is necessary to use long shebolts to connect the vertical stiff-backs or strong-backs that produce tension to compress and hold the form in the desired position. These shebolts are heavily greased, and must be pushed through holes in the beams and forms by workers clinging to the beams. These activities often involve the workers applying pressure to the form which tends to push the worker outwardly away from the form, thereby risking serious injury or death due to falls from great heights.
Climbers have sometimes used safety lines and harnesses with snap links or spring-loaded carabiners for protection, either wrapping a section of the safety line around a structural member, or more frequently hooking the safety link over the edge or into the slot of a beam. However, the normal movement of climbing the beams or scaffolding and working on the forms will cause the safety links to "roll-out" without the worker being aware or in a position to reset the link, thereby rendering the safety line useless. Similarly, wrapping a section of the safety line around a structural member may not provide the necessary strength to catch the worker in a fall if the line is positioned improperly, and wrapping or unwrapping the line generally requires two hands which often places the worker in a precarious position.
Various camming, jumar, and friends-type devices are known in the art for mountaineering. However, these mountaineering devices are not particularly suited for use as anchors on slotted or conventional beams or the other components of a concrete pouring form, and are not constructed to withstand the rigors and abuses associated with use in a heavy construction environment. Some of the devices particularly suited for window washers and painters are heavy-duty adaptations of mountaineering equipment, but generally relate to ascenders or jumars that may be attached to a tensioned vertical safety line and connected to a harness.
U.S. Pat. Nos. 3,348,632 to Swager and 4,767,091 to Cuny each disclose devices that slide along and clamp the flat face of a conventional I-beam or ride on and grip the edge surfaces of the flanges, the Cuny '091 patent disclosing pivoting side portions which permit attachment of the device to the beam. However, the device disclosed in Cuny '091 requires that a ring hold the two pivoting side portions together, and any slack or play in that ring can allow the sides to disengage from the beam. This is particularly true if an eccentric ring is used. The safety devices of Swager '632 and Cuny '091 are not designed for rapid or one-handed attachment or removal from the beams, and are oriented to clamp and cam against a vertical rather than a horizontal beam. Moreover, while the safety device of Cuny '091 is designed to wedge against the beam in case of a fall, the force of any fall is transferred directly to the pivot pin connecting the pivoting side portions, thereby weakening the device considerably.
U.S. Pat. No. 3,933,220 to Swager discloses a clamping device which is received through a slot in a vertical rail and which wedges or clamps against the interior of that rail under the weight of a fall, but which is not designed to be readily removed or disengaged from the rail.